On Fri, May 31, 2024 at 12:04 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Tue, May 28, 2024 at 5:25 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
> >
> > Share relocation implementation with the kernel. As part of this,
> > we also need the type/string visitation functions so add them to a
> > btf_common.c file that also gets shared with the kernel. Relocation
> > code in kernel and userspace is identical save for the impementation
> > of the reparenting of split BTF to the relocated base BTF and
> > retrieval of BTF header from "struct btf"; these small functions
> > need separate user-space and kernel implementations.
> >
> > One other wrinkle on the kernel side is we have to map .BTF.ids in
> > modules as they were generated with the type ids used at BTF encoding
> > time. btf_relocate() optionally returns an array mapping from old BTF
> > ids to relocated ids, so we use that to fix up these references where
> > needed for kfuncs.
> >
> > Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> > ---
> > include/linux/btf.h | 45 ++++++++++
> > kernel/bpf/Makefile | 10 ++-
> > kernel/bpf/btf.c | 168 +++++++++++++++++++++++++----------
> > tools/lib/bpf/Build | 2 +-
> > tools/lib/bpf/btf.c | 130 ---------------------------
> > tools/lib/bpf/btf_iter.c | 143 +++++++++++++++++++++++++++++
> > tools/lib/bpf/btf_relocate.c | 23 +++++
> > 7 files changed, 344 insertions(+), 177 deletions(-)
> > create mode 100644 tools/lib/bpf/btf_iter.c
> >
>
> [...]
>
> > +static inline struct btf_decl_tag *btf_decl_tag(const struct btf_type *t)
> > +{
> > + return (struct btf_decl_tag *)(t + 1);
> > +}
> > +
> > static inline int btf_id_cmp_func(const void *a, const void *b)
> > {
> > const int *pa = a, *pb = b;
> > @@ -515,9 +528,17 @@ static inline const struct bpf_struct_ops_desc *bpf_struct_ops_find(struct btf *
> > }
> > #endif
> >
> > +typedef int (*type_id_visit_fn)(__u32 *type_id, void *ctx);
> > +typedef int (*str_off_visit_fn)(__u32 *str_off, void *ctx);
> > +
>
> let me take a quick stab at implementing type/str field iterator in
> libbpf. If I don't get stuck anywhere, maybe you can just rebase on
> that and avoid the callback hell and the need for this
> callback-vs-iter churn in the kernel code as well
>
Sent it out as one RFC patch (which unfortunately makes it harder to
see iterator logic, sorry; but I ran out of time to split it
properly), see [0].
It is especially nice when per-field logic is very simple (like
bpftool's gen.c logic, where we just remap ID). Please take a look and
let me know what you think.
[0] https://patchwork.kernel.org/project/netdevbpf/patch/20240601014505.3443241-1-andrii@xxxxxxxxxx/
> > #ifdef CONFIG_BPF_SYSCALL
> > const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
> > +void btf_set_base_btf(struct btf *btf, const struct btf *base_btf);
> > +int btf_relocate(struct btf *btf, const struct btf *base_btf, __u32 **map_ids);
> > +int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ctx);
> > +int btf_type_visit_str_offs(struct btf_type *t, str_off_visit_fn visit, void *ctx);
> > const char *btf_name_by_offset(const struct btf *btf, u32 offset);
> > +const char *btf_str_by_offset(const struct btf *btf, u32 offset);
> > struct btf *btf_parse_vmlinux(void);
> > struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog);
> > u32 *btf_kfunc_id_set_contains(const struct btf *btf, u32 kfunc_btf_id,
>
> [...]
